1. Field of the Invention
The invention relates to a railway car truck incorporating a novel transom, which provides the truck with a soft spring rate vertically as compared to a truck having a conventional spring plank or transom design, yet with a desired rigidity laterally and longitudinally, with a corresponding improvement in truck performance.
2. Description of the Related Art
The conventional railway freight car truck in use in North America for several decades has been the three piece truck, comprising a pair of parallel side frames connected by a transversely mounted bolster. The bolster is supported on the side frames by spring sets. The wheelsets of the truck are received in bearing adapters placed in leading and trailing pedestal jaws in the side frame, so that axles of the wheelsets are parallel. The railway car is mounted on the center plate of the bolster, which allows the truck to pivot with respect to the car. The spring sets permit the side frames to move somewhat with respect to the bolster, about the longitudinal, vertical and transverse axes.
It has long been desired to improve the performance of the three piece truck. Resistance to lateral and longitudinal loads and truck performance can be characterized in terms of one or more of the following well-known phenomena.
“Parallelogramming” occurs when one side frame moves forward longitudinally with respect to the other, such that the inboard and outboard wheel sets remain parallel to each other but they are not perpendicular to the rails, as may happen when a railway car truck encounters a turn.
“Hunting” describes an oscillating lateral movement of the wheelsets that causes the railcar to move side-to-side. Hunting may be dangerous when the oscillations attain a resonant frequency. Hunting is more likely to occur when there is a lack of proper alignment in the truck as made, or developed over time through various operating conditions. Hunting is also more likely to occur when the railcar is operated at higher speeds. The speed at which hunting is observed to occur is referred to as the “hunting threshold.”
Several approaches have been tried to improve the lateral stability of the standard three piece truck to prevent parallelogramming and hunting, while at the same time ensuring that the truck is able to deform appropriately to accommodate the different distances traveled by the wheels on the inside and outside of a turn, respectively. Conventionally, a “spring plank” was laid on the side frames underneath the springs to prevent parallelogramming of the truck. The spring plank was kept in place by the weight of the overlying freight car on the bolster through the spring sets. Spring planks came to be used less frequency after roller bearings replaced journal bearings in wide usage. However, some truck designs continued to utilize variations of the transom or spring plank concept, as described below.
U.S. Pat. No. 3,461,814 to Weber references several milestones in the history of the spring plank, and discloses an improvement thereon referred to as a “roll control” truck. In the roll control truck, a spring plank is positioned on the spring seats of the side frames and is provided with an aperture for receiving a lug protruding downward from the bolster. The engagement of the bolster with the spring plank via the lug at this low point ensures that lateral forces are transferred to the side frames at a lower point on the truck, closer to the rails, which according to the patentee, improves car roll performance. The position of the spring plank underneath the springs in the spring seat of the side frame is typical of the prior art spring plank.
U.S. Pat. No. 3,670,660, also to Weber, discloses a “swing motion” truck, which is a modification of the roll control truck, wherein a rocker seat is interposed between the spring plank and the side frame, along with “rockably journaled” roller bearing adapters, which enables the side frames to rock in unison to accommodate lateral forces. As with the aforementioned roll control truck, the swing motion truck is characterized by the position of the spring plank over the spring seats of the side frames.
In a later development of the swing motion truck, described in U.S. Pat. No. 5,027,716, also to Weber, the patentee noted certain drawbacks of the swing motion truck, specifically in the mating of the rocker seat and the transom, which tended to reduce the rigidity of the truck average. In the design depicted in the '716 patent, the springs are seated directly on the rocker seat, and the spring plank is replaced with a pair of transverse support rods received in anchor brackets with elastomeric pads, such that the rocker seats are interconnected by the support rods to provide lateral rigidity to the truck.
Also known in the art are so-called “steerable” trucks, which allow a degree of rotation of each wheelset about a vertical axis so that the wheelsets may take an out-of-square position with respect to a longitudinal axis of the truck, permitting a truck to negotiate a turn. The invention described herein may be used with steerable and non-steerable trucks. U.S. Pat. No. 4,003,316 to Monselle, for example, depicts a type of steerable truck having a transom/bolster assembly, with elastomeric pads provided in the side frame opening between the transom/bolster assembly and the side frame for wheel load equalization. Combining the bolster and transom in the manner of the '316 patent adds complexity to the truck design and complicates the servicing of the truck parts. The steering mechanism itself is also complicated and costly.
U.S. Pat. No. 4,131,069, to List, also discloses a steerable truck, and is more typical of steerable truck designs generally. In the disclosed embodiments, the wheelsets of a truck are joined by an arm which controls and maintains the relationship between the wheelsets. The arm is further connected to a body of the railroad car so that movement between the car body and the wheelsets is maintained in a fixed relationship. In this case the steering arms, rather than a spring plank or transom, provide the lateral rigidity, which according to the patentee, is required to avoid hunting.
U.S. Pat. No. 4,483,253, also to List, describes a retrofit of then existing truck designs (i.e., for non-steerable trucks) which is said by the patentee to provide some of the advantages of the steerable truck at lower cost. The '253 patent discloses using a spring plank connecting the side frames of a truck provide lateral stability in combination with elastomeric pads provided in the pedestal jaws to provide some flexibility between the axles and the side frames of a truck. This combination is presented as a retrofit to then existing truck designs, which is alleged by the patentee to provide a non-steerable truck with better turn-negotiating capability. The spring plank is located in the conventional manner under the springs or ridgidly connected to each side frame.
U.S. Pat. No. 4,938,152, also to List, is in the same patent family as the aforesaid U.S. Pat. Nos. 4,131,069 and 4,483,253, and also contains additional disclosure. The '152 patent contemplates truck designs including a “shear plate,” or transom, rigidly connecting the side frames and elastomeric pads in the pedestal jaws of the truck. Several modes of attaching the shear plate to the side frames are disclosed, so that it is not necessary to lay the shear plate under the springs. However, in all cases, the connection between the shear plate and the side frames is required to be completely rigid and the shear plate is located beneath the bolster, which creates another potential clearance problem.
Diagonal braces have been tried as an alternative to the conventional transom to provide resistance to parallelogramming while at the same time providing flexibility to adjust for the farces encountered on a curve. U.S. Pat. Nos. 5,461,986 and 4,570,544 both disclose diagonal brace designs. In both cases, the diagonal members utilize brackets to attach to the side frame. Brackets are needed to pitch the braces beneath the bolster. One drawback of diagonal braces is that they cross in the middle and therefore must be located underneath the bolster which creates a problem with respect to clearance. Alternatively, a means is provided to attach the braces to the bolster where the braces cross. In some cases, through holes have been provided in the bolster to accommodate the braces, which may weaken the bolster.
In light of the foregoing, one object of the invention is to provide rigidity to a three piece truck without impacting vertical clearance between the truck and the track. This clearance is set by AAR standards, in any event, and may not be less than 2¾ inches with springs solid and with maximum wear condition.
Another object of the invention is to provide a transom which provides rigidity to the truck while still providing sufficient torsional flexibility so that the truck meets the AAR wheel load equalization requirements.
Still another object of the invention is to provide a transom which does not interfere with the operation of the springs, the brake or other equipment associated with the truck.
In yet another aspect, the invention is directed to an improved truck, including the transom as described herein, and also including a modified bearing adapter wheelset interconnection, which provides a controlled ratio of lateral versus longitudinal spring rate between the side frames and bearing adapter, as described in co-pending application Ser. No. 13/600,693, filed on even date herewith and incorporated by reference in its entirety.
These and other objects of the invention are achieved according to the invention as follows.